Powdered metal casing for perforating charge and its method of manufacture

ABSTRACT

Disclosed herein is a powdered metal casing and an apparatus and method for making the powdered metal casing, which casing is useful for shaped explosive charges for perforating oil and gas wells.

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to a casing for shaped explosive charges for usein perforating oil and gas wells, and its method of manufacture.

The use of shaped charges for perforating in oil wells is well known.Such shaped charges include a bell shaped housing or casing into whichis inserted a cone shaped liner with explosive material therebetween.The shaped charge is then located in the tubular housing of aperforating gun and oriented such that when the explosive is detonatedthe conical liner is destroyed and a jet is formed which is directedthrough a port in the housing of the gun to perform the desiredperforating.

In a nonexpendable gun the port is sealed with a replaceable plug suchthat after perforation the gun assembly may be retrieved and new shapedcharges and port plugs may be installed such that the gun assembly maybe reused.

The explosions of the shaped charge to perform the perforatingoperations tends to cause swelling and distortion in the gun housing.Because of these distortions, the life of the gun housing may beshortened such that the gun housing must be discarded after a few uses.

Several attempts in the past have been made to reduce damage to the gunhousing without affecting the performance of the shaped charge. One suchattempt to increase the life of the gun housing is shown in U.S. Pat.No. 3,282,354 to Hakala et al wherein a double walled case was usedaround the shaped charge.

In the past, pressed metal liners have been used for insertion into amachined steel casing to form the shaped charge.

In the present invention a pressed powdered metal casing is disclosedfor use with a shaped charge in an oil well perforating gun, whichcasing is destroyed with the detonation of the explosive material. Ithas been found that use of the pressed powder metal casing results inless distortion and damage to the perforator gun housing.

It has also been found that the pressed metal casing is reduced to apowder by the explosion of the shaped charge. This powder is easilyremovable from the perforator gun housing when the housing is beingcleaned for reuse.

It has further been found that the use of heavier metals in the pressedmetal casing for the shaped charge results in deeper perforations thanwhen a lighter metal, for instance iron, is used. It has also been foundthat when a lighter metal such as iron is used, less distortion of theperforator gun housing results.

Also disclosed is a molding apparatus and components of a powdered metalmix which may be used in forming the shaped charge housing of theinvention.

THE DRAWINGS

A brief description of the appended drawings follows:

FIG. 1 provides a horizontally sectioned view of the perforator gunassembly with the shaped charge in place and sectioned.

FIG. 2 shows an apparatus for compressing the shaped charge housing withthe apparatus in the loading position.

FIG. 3 shows the apparatus of FIG. 2 in the loaded position before thecompression step.

FIG. 4 shows the apparatus of FIGS. 2 and 3 in the fully compressedposition wherein the pressed metal casing of the shaped charge isformed.

Shown in FIG. 1 is a cross-section of a reusable perforating gunincluding a hollow carrier 10 which is a tube or a pipe having aninterior bore 11 therethrough. Located in the interior bore 11 is ashaped charge apparatus 12. As is known in the art, the shaped chargeapparatus 12 may be one of a plurality of charges spaced within thehollow carrier 10 in a desired orientation and distribution.

The shaped charge assembly 12 includes a powdered metal housing 15, acharge liner 16 forming a cone extending into the housing 15 as is knownin the art, and explosive material 17 disposed between the charge liner16 and the housing 15.

A hole 18 is provided through the rear of the housing 15 immediatelyopposite the apex of the cone of the charge liner 16 and has locatedtherein a booster 19 for detonating the explosive material 17. Theshaped charge assembly 12 is covered with a rubber covering having arear portion 20 and a forward portion 21 cemented over the housing 15 asis shown in FIG. 1. The forward portion 21 of the rubber coveringprovides the desired stand off for forming a jet of hot gases from thedetonation of explosive 17.

A port 24 is provided through the hollow carrier 10 and is sealed by anappropriate plug means such as the threaded port plug 25. A sealingwasher 26 is located between the port plug 25 and the hollow carrier 10and is compressed by the threaded connection between the port plug 25and port 24 such that a fluid tight seal is established between theexterior of the hollow carrier 10 and the interior bore 11 of thecarrier.

Means are additionally provided in the charge carrier 10 to locate theshaped charge assembly 12 in the desired orientation such that the jetof hot gases is directed through the port plug for perforation of theoil well as desired. This centering means is shown in FIG. 1 as recess27 into which a corresponding projection of the rear rubber covering 20extends in order that the shaped charge is held in the desiredorientation.

A hole 29 passes through the rear rubber covering portion 20 at rightangles to the axis of rotation of the charge liner 16 and the housing15, and is adjacent to the booster charge 19. Primacord 30 is passedthrough the hole 29 and likewise passes through other shaped chargeassemblies in the hollow carrier 10. The primacord 30 is initiated by asuitable detonating device such that when the primacord is detonated thebooster charge 19 is in turn detonated for igniting the explosive charge17 to form the desired jet of the perforator.

The hollow carrier 10 is dimensioned such and is of sufficient strengththat the hollow carrier 10 may be used repeatedly for severalperforating operations.

Shown in FIG. 2 is an apparatus which may be used in pressing thepowdered metal housing 15. The apparatus in FIG. 2 is shown in theloaded position, and includes an anvil 35 having a pedestal 36 uponwhich is mounted an interior mold 37 having the shape of the interiorwalls of the finished housing 15. Arranged over the interior mold 37 isa mold housing 38 having an interior mold chamber 39 surrounding theinterior mold 37. The interior walls 40 of the mold chamber 39 have theshape of the outer walls of the housing 15. The pedestal 36 of the anvil35 is fitted into the molding chamber 39 of the mold housing 38, andslidable movement is allowed at 41 between the pedestal 36 and thehousing 38 without passing a powdered metal mix in the molding chamber39.

In the upper portion of mold housing 38 is a loading chamber 43. Aloading port 44 is provided through the mold housing 38 and into loadingchamber 43 for the entry of powdered metal mix into the loading chamber43.

A plunger 46 is centered in the loading chamber 43 and is arranged suchthat when the plunger 46 is lowered into the necked down portion 48 ofthe housing 38, a tight engagement between the portion 48 and theplunger 46 is established such that powdered mix may not pass betweenchambers 43 and 39 when the plunger 46 is in its lower position in thenecked down portion 48.

A centering and sealing means 49 is provided in the upper end of moldhousing 38 around plunger 46 to center plunger 46 in the desiredlocation in chamber 43 and to prevent passage of mix between the plunger46 and the housing 38.

It will be seen that when powdered mix is injected into loading port 44,the mix flows into loading chamber 43 and through the necked downportion 48 into the mold chamber 40 when the plunger is in the positionshown in FIG. 2.

FIG. 3 shows the molding apparatus in the cut off or loaded positionjust prior to compression of the powdered metal mix in the moldingchamber 39. The plunger 46 has been moved to a lower position whereinthe bottom end of plunger 46 is in the necked down portion 48 of themold housing 38 to cut off the flow of powdered metal mix between thechambers 43 and 39. It will be understood that in that position, theplunger 46 forms one end of the mold chamber 39 for forming the rear endof the casing 15.

The molding apparatus is shown in FIG. 4 in the compressed positionwherein the housing 15 is fully compressed to its desired shape. Toarrive at this position, the plunger 46 and the mold housing 38 are bothmoved downwardly together and the powdered metal mix in molding chamber39 is compressed until an approximate load of 120,000 pounds per squareinch is exerted on the powder.

A projection may be provided at 52 on the end of plunger 46 to cut thehole 18 in the rear of the powdered metal casing 15 or hole 18 may bepunched or drilled into the rear of the casing 15 by a separateoperation as desired.

After the compressing operation is complete, the mold housing 38 and theplunger 46 are raised, and the now compressed casing, by virtue of thefriction between walls 40 and the compressed casing, remains in moldingchamber 39 and is raised with the housing 38. The finished casing isthen ejected from the molding chamber 39 by lowering the plunger 46 topunch out the casing into an appropriate receiving means.

The molding apparatus is then returned to the loading position shown inFIG. 2 for a repeat of the operation to form another compressed powderedmetal casing.

The powdered metal mix is composed of about 80 percent by weight of apowdered metal having a diameter of approximately 100 microns, 19percent by weight of lead powder having a diameter of approximately 100microns, and one percent by weight of graphite powder. The powderedcomponents of the mix are available from Glidden Metals at 900 UnionCommerce Building, Cleveland, Ohio 44115. The lead powder is identifiedas Glidden 100-B and the graphite powder is identified as Glidden No.1645. Iron powder identified as Glidden B-214 may be used in the mix, orcopper powder identified as Glidden 100 RXM may be used as desired.

It has been found that a pressed powder casing of a metal with a higheratomic number used with the same amount of explosive material results indeeper penetration of a beria target in a standard test. The followingtable shows the resulting penetrations into a beria target of a machinedsteel casing, pressed iron casing and a pressed copper casing, each usedin a 31/8" outside diameter gun.

    ______________________________________                                        Machined Steel                                                                             Pressed Iron Pressed Copper                                      ______________________________________                                        Shot 1  9.14"    Shot 1   7.60" Shot 1 10.04"                                 Shot 2  10.81"   Shot 2   8.30" Shot 2 8.26"                                  Shot 3  7.62"    Shot 3   6.95" Shot 3 8.10"                                  Avg.    9.19"    Avg.     7.62" Avg.   8.80"                                  ______________________________________                                    

It can be seen that the penetration of a gun using a pressed coppercasing is generally superior to that of pressed iron, and is about thesame as a conventional machined steel casing.

It has also been found that a pressed powder casing of a metal with alower atomic number used with the same amount of explosive materialresults in less carrier expansion. The following table gives acomparison of the resulting carrier expansions for machined steel,pressed iron, and pressed copper casings, each used with a 31/8" outsidediameter gun.

    ______________________________________                                        Machined Steel                                                                             Pressed Iron Pressed Copper                                      ______________________________________                                        Shot 1  .012"    Shot 1   .010" Shot 1 .007"                                  Shot 2  .016"    Shot 2   .015" Shot 2 .026"                                  Shot 3  .024"    Shot 3   .016" Shot 3 .020"                                  Avg.    .017"    Avg.     .014" Avg.   .018"                                  ______________________________________                                    

It can thus be seen that the carrier expansion of a gun using a pressediron casing is generally less than that of a pressed copper or amachined steel casing. It can also be seen that the carrier expansionfor a gun using pressed copper casings is about the same as one havingmachined steel casings.

The pressed metal casing of the shaped charge of the invention is onewhich is inexpensive to fabricate and which provides a precision casing.When the shaped charge is detonated, the casing absorbs some of theenergy of the exploding charge for reducing the casing to a powder. Thepowder residue resulting from the destruction of the powdered metalcasing is more easily cleaned from the hollow carrier in preparing thecarrier for later perforation operations. The case is compressedsufficiently to provide a green compact and is not sintered, thus theprecision of the casing is maintained since there is no shrinkage ordistortion caused by a heating or sintering process.

By using shaped charges having pressed powder metal casings using ametal having a lower atomic number such as iron, less distortion isimparted to the hollow carrier giving the carrier longer life.

By using shaped charges having pressed powder metal casing using a metalhaving a higher atomic number such as copper, the penetration of theshaped charge is increased to be about the same as the penetration of amachined steel casing, while retaining the advantages of simpleness offabrication and low cost in making a precision casing.

The foregoing embodiments, such as the constituents, composition, andsizes of the powdered mix, have been disclosed as illustrativeembodiments of the invention. Changes and modifications of theseembodiments will be apparent to those skilled in the art. The appendedclaims are intended to cover such equivalent embodiment which may fallwithin the true spirit and scope of this invention.

What is claimed is:
 1. A shaped charge casing formed solely of a greencompact consisting of powdered metal sufficiently compressed to form ajet upon explosion of said shaped charge while being reduced to a powderby said explosion.
 2. The casing of claim 1 wherein said powdered metalis compressed to approximately 120,000 PSI.
 3. The casing of claim 1wherein said compact is composed of about 80 percent by weight of apowdered metal having a diameter of approximately 100 microns, about 19percent by weight of powdered lead having a diameter of approximately100 microns, and about one percent by weight of graphite powder.
 4. Thecasing of claim 3 wherein said powdered metal has an atomic number atleast as great as iron.